1. Field of the Invention
The present invention relates to a new and improved super abrasive saw blade for separating packaged semiconductor devices one from another. More particularly, the present invention relates to a thin self-sharpening and self-cleaning singulation saw blade that cuts faster and lasts longer than prior art saw blades.
2. Description of the Prior Art
Saw blades for dicing silicon ingots and wafers are known. Most of these prior art blades are electro deposited, metal bonded by brazing or sintering or resin impregnated and contain natural or synthetic diamonds. None of these prior art blades are suitable for singulating or separating new high volume packaged devices that are mounted on lead frames or PC boards or substrates used in matrix array packaging.
Presently, high volume production packaged semiconductors are predominately small outline integrated circuit (SOIC) packages or Quad Flat Packs (QFP). Typical memory devices such as TSOP are die attached to lead frames to provide leaded plastic devices. The leads are then formed as flexible gull wing legs that are mounted on substrates or PC boards.
The new high volume production devices usually combine several functions on one chip. Such devices as personal digital assistants (PDA), small hand computers such as Palm Tops™, personal organizers, wireless phones with non-phone features and global positioning (GPS) devices all use new integrated functionability and require more complex electronics in one integrated package or chip. To meet the new requirement for integrated digital signal processing chips (DSP) and to continue increased data speeds while lowering cost and reducing size, new small DSP chips with high density and multiple functions are being manufactured in the form of matrix array leadless packaging. New matrix array leadless packages are known to be more cost effective to manufacture, however, the individual packages on some forms of carriers cannot be effectively separated one from another using silicon wafer dicing saw technology or other abrasive blade technology. Prior art dicing saw blades are designed to cut or grind through a wafer of silicon to separate die one from another and most use some form of liquid cooling agent or very pure water. In contrast thereto matrix array leadless packages such as Micro Lead Frame (MFL) packages and Quad, Flat, No-lead (QFN) all contain multiple layers which may comprise soft conductive metal, fiberglass and sheets of plastic that encapsulate the plural packages of a matrix array.
Diamond impregnated resinoid saw blades or metal bonded blades have been tried. They are thick (0.007 to 0.015 inches) and have high cost and short life and to some extent have excessive side wear.
Metal bonded and sintered compacted blades are also thick and tend to wear to a bullet nose shape creating a taper cut that is unacceptable because it changes the dimension of the package.
Thin electrodeposited dicing saw blades may tear and the cutting efficiency degrades quickly when cutting matrix array type materials. This degrade of cutting efficiency requires frequent blade replacement. Each time the blade is replaced it is restarted at a slower cutting feed rate.
The above-mentioned dicing saw blades tend to clog or load up with resin and soft metal. Clogged blades cut slower and increase heat at the edges of the blade which results in destruction of the packages or the soft metal and plastic becomes so hot that it smears. When the smears create burrs on the package they can be rejected for being out of specification. Some burrs may be removed in secondary operations to save the package or device at added cost.
Most of the above-mentioned dicing saw blades were found to cut slower, cost more, require removal and redressing and cannot be depended upon for a full production shift of manufacturing acceptable matrix array leadless packages.
Therefore, it is highly desirable to provide a new and improved singulation saw blade for separating packages in a matrix array, that cuts fast, is self-cleaning, cuts cool enough as not to always require a surfactant or water coolant, does not load or clog, does not produce out of specification burrs and is longer lasting.